A known crash box serving as an impact-absorbing device for a vehicle is disclosed in JP2005-225394A (i.e., hereinafter referred to as Patent reference 1). The known impact-absorbing device disclosed in the Patent reference 1 is made from a forged member made of aluminum alloy and integrally includes a cylindrical impact-absorbing portion having a constant cross section in an axial direction, a bumper side attaching portion for closing one of end openings of the impact-absorbing portion, and a vehicle body side attaching portion formed in a flange shape which extends from the other of end openings of the impact-absorbing portion.
Another known crash box disclosed in JP2005-1462A (i.e., hereinafter referred to as Patent reference 2) is made from a forged member made of aluminum alloy and integrally includes a cylindrical impact-absorbing portion having a constant cross-section in an axial direction, a bumper side attaching portion for closing one of end openings of the impact-absorbing portion, and a cylindrical vehicle body side attaching portion extending in an axial direction from the other end openings of the impact-absorbing portion.
A known crash box disclosed in JP2005-271858A (i.e., hereinafter referred to as Patent reference 3) includes a cylindrical impact-absorbing portion made from an extrusion member made of aluminum alloy, a plate-shaped bumper side attaching portion for closing one of end openings of the impact-absorbing portion, and a plate-shaped vehicle body side attaching portion for closing the other of end openings of the impact-absorbing portion. The impact-absorbing portion, the bumper side attaching portion, and the vehicle body side attaching portion are, for example, connected by welding.
With the constructions disclosed in Patent reference 1 and Patent reference 2, a configuration of material for the forging and freedom of design in configuration are limited. Because the impact absorbing device disclosed in the Patent reference 1 and the Patent reference 2 cannot be formed only by a forging process, it is assumed that a pressing process, or the like, may be required after the forging process. Thus, manufacturing hours and manufacturing costs are increased.
The crash box disclosed in the Patent reference 3 includes three separate members, that is, the impact-absorbing portion, the bumper side-attaching portion, and the vehicle body side attaching portion, and thus requiring a welding process for connecting the separate members. This increases the manufacturing hours and manufacturing costs. Further, because the impact-absorbing portion is made by extrusion, a configuration of the impact-absorbing portion is limited to have a constant cross-section in an axial direction.
JP2001-198659A (i.e., referred to as Patent reference 4) discloses an aluminum alloy member which is applicable to casting of the crash box. The aluminum alloy member disclosed in the Patent reference 4 is Al—Si alloy which is similar to an eutectic composition, which excels in castability. However, because Sr is not added in the aluminum alloy member disclosed in the Patent reference 4, the refinement of the eutectic Si phase is likely to be inadequate and a ductility of a cast member (crash box) may decline.
A need thus exists for an impact absorbing device for a vehicle and a bumper device for a vehicle which is not susceptible to the drawback mentioned above.